The invention relates to a brake disc assembly particularly for large industrial brake discs having air cooling passages.
Large industrial brake discs, that is brake discs that exceed 0.5 meters in diameter and are capable of absorbing large amounts of power, are commonly provided with air cooling passages. The air cooling passages extend radially from an inlet generally adjacent the center of the disc to an outlet adjacent a periphery of the disc. The passages pass between surfaces of the disc that are to be swept by brake shoes. As the disc rotates, air is sucked into the inlet, and discharged from the periphery somewhat in the manner of a centrifugal pump. Air passing through the passages between the surfaces removes heat generated during braking. Temperature variations across the disc produce inequal expansion and contraction, which can cause serious distortion of the disc and consequent erratic braking.
Commonly, discs of this size are manufactured by sand casting as a single piece, using expendable cores to produce the air cooling passages within the disc. Difficulties can be encountered when casting large discs, particularly to produce a sound casting without "cold-shuts" or "mis-runs" in relatively thin internal webs or walls between the air cooling passages. Large discs of this type can also be difficult to cast and concurrently maintain material integrity, in which the material is free of mold inclusions and oxide inclusions, which is necessary for discs which rotate at high speeds and absorb large amounts of horsepower. The rough-cast disc is machined to produce smooth annular braking surfaces on each side of the disc. The cost of manufacturing such discs can be quite high due to the high scrap rates, and salvaging costs of poorly cast discs. If a portion of the one-piece cast disc cannot be salvaged, the whole disc is rejected, thus increasing manufacturing costs.